


a brick-boot swimming lesson (in the deep end of my adolescence)

by cashtastrophe



Series: goddamn, we missed the vein [7]
Category: Undertale (Video Game)
Genre: Abuse, Angst, Bondage, Child Abuse, Dehumanization, Drugs, Ecto-Genitalia (Undertale), Ecto-Vagina (Undertale), Fingering, Humiliation, Incest, M/M, Medical Kink, Parent/Child Incest, Past Rape/Non-con, Porn, Pseudo-Incest, Sibling Incest, gagging, papyrus is a tiny creep, welp, who grows into a bigger creep
Language: English
Status: In-Progress
Published: 2017-03-16
Updated: 2017-03-19
Packaged: 2018-10-06 08:21:32
Rating: Explicit
Warnings: Graphic Depictions Of Violence, Rape/Non-Con, Underage
Chapters: 2
Words: 4,318
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10330286
Author URL: https://archiveofourown.org/users/cashtastrophe/pseuds/cashtastrophe
Summary: That Time in the Basement—and he always thinks of it like that after, capitals and all—isn't even close to the first time he's caught them.It's the first either of them knows about, probably, because Papyrus is small and limber and very good at hiding in small spaces, and also at being quiet when he really has to, if only then.(a request from tumblr for the fell bro's First Time that's just gotten real out of hand and real gross.)





	1. Chapter 1

**Author's Note:**

> boy howdy uh
> 
> welp. so this is gonna be the party from little blue pills here eventually. stay tuned.

Undyne isn't especially pretty, even allowing for some necessary subjectivity when Papyrus considers the fact that she's an entirely separate species from him.  
  
...not that he's even actually seen a female skeleton in person to compare her to, but still. The point stands.  
  
She's big for her age, nearly as tall as Papyrus himself and broad-shouldered besides, her long limbs ropy with muscle. She doesn't walk with any sway to her narrow hips at all, decidedly unlike most of the other girls in their class. Any evidence of her small breasts is usually hidden under outsized t-shirts, though he doesn't think it's deliberate, only that she shares his brother's penchant for clothing that serves both as daywear and pajamas.  
  
She's willowy though, graceful in spite of her size, very much unlike her mother's compact build. He assumes she gets it from her father, must take after him, though he has no idea what the guy looks like.   
  
No idea if he's a fish monster, even, come to think of it. Is that...is that how that works? Do monsters necessarily _have_ to breed with their own kind? Undyne and her mom both kinda look like lanternfish, does that mean Melusine _absorbed_ her mate or—? Would he and Undyne even be able to—?  
  
He shakes his head furiously. As always, he's getting ten steps ahead of himself.  
  
_Anyways_.  
  
The fight that had left Undyne's left eye milky and sightless had ruined the flesh of that cheek as well, broad claw-marks dragging down the ridge of her eye socket to terminate dramatically along the shaved side of her head. She normally hides it beneath the riot of bright-red hair she never manages to contain entirely in her ponytail, but he can still see it if he watches for it, especially when she flicks her bangs impatiently out of her face.  
  
That's the thing Papyrus finds himself staring at most often, actually, the silvery-blue stripes of the scars against the delicate skin of her bare skull. She's lucky, he thinks, though he knows better than to say as much, knows it would make her wrinkle her brow at him in that narrow, calculating way he hates. It's a beautiful mark across a prominent feature, though, and it certainly makes her look older than her sixteen years. Makes her look tough. Formidable.  
  
(nothing at all like the deep black nothing of the fracture in sans's skull, the ragged chunk of missing bone gaping empty and horrible where Gaster had slammed his head into the kitchen tile, over and over and over until the resulting _crack_ sounded sick-wet with blood, meaty, _unbearable,_ until sans had gone limp and compliant and moaned _i'm sorry, i'm sorry, please just_ stop—)  
  
She blinks when she looks in the mirror, though, wide-eyed, her mouth dropping just slightly open to expose the tips of her incisors. Her claws, painted a chipped black she's not bothered to touch up in _weeks_ , skim along the edge of the scars, mapping out the familiar lines which he's highlighted in a kind of shimmering hot-pink makeup.  
  
It catches the light strikingly across her high cheekbone, makes it look like she's bleeding glitter from a fresh injury. Makes her look surreal, almost, alien and fierce and untouchable. Her lips twist into a bright, crooked smile when she realizes what the color is meant to simulate, sees the tracks “dripping” down the angle of her jaw, the curve of her throat.  
  
Papyrus has even done her hair for her, swept it neatly out of her face and away from her scars into a loose, complicated braid snaking over her right shoulder. He's highlighted the lid of her good eye in the same color as the “blood,” just a simple sweeping line that does not detract at all from the riot he's made of the other half of her face.  
  
“ _Dude_ ,” she says, sounding positively awed and flicking her eyes to his, so sweet and grateful and genuine that it makes him grit his filed teeth hard enough to ache. She punches him on the shoulder, though Papyrus braces for it, and barely winces. He just scowls kind of affectionately down at her and busies himself screwing the lid back onto the tiny pot of makeup. He's hoping she'll be too distracted by her own reflection to bother asking what he's doing with the stuff under his bed.  
  
She doesn't say anything, but she does brush a wide swath of leftover pink beneath his right socket along the faint fault-lines where Gaster had once broken his zygomatic process with a particularly harsh backhand. He doesn't see it coming this time, she's on him so fast. He's only able to be distantly proud that he doesn't actually flinch back from the touch past the alarm bells her abrupt proximity sound inside his head. He catches himself just in time, though he sucks in a sharp, surprised breath when she makes contact.  
  
“There,” she says, and dusts her hands off, sparkles flaking like acid-trip snowflakes onto her ragged black jeans. “Now we match. Like war paint, huh?”  
  
He knows very well that she phrases it like that for his benefit. He knows her tricks by now, sees very clearly how she is careful to frame it in a context he might find acceptably masculine and aggressive— though she can't have missed the myriad of small jars and brushes in the box he's kicked beneath his mattress. It's far more, far too varied for the kind of finger-painting she'd smeared messily across his cheek.  
  
“Yeah,” he says instead of anything remotely useful. He's not wearing his boots. His toe-claws are painted a shimmering blue that's upsettingly close to the color of Undyne's scales.   
  
She hasn't said anything about that, either.  
  
“Is sans coming?” Undyne hops off the top of his dresser, landing catlike on her feet.  
  
“Why would he?”  
  
“Seems like he'd be fun at a party, I dunno. He's a cool guy.” She retrieves her leather jacket from the floor where she'd dropped it and shrugs it back on, careful not to brush against the makeup, as thought it is paint that still needs to dry. From an inside pocket she fishes a lighter and a small baggie, tossing the latter to Papyrus, who catches it without thinking.  
  
He frowns and holds it up to examine, squinting his sockets at the handful of lavender pills inside. They're small, perfectly round, each stamped with a neat little question mark. “Undyne— “  
  
“Oh, shut up.” She folds her arms across her chest and draws herselfstubborn up to her full height, scowls. “Look, just—I know it's not your _thing_ , okay, but you need to loosen up. Chill out a bit. Make some kind of attempt at enjoying yourself, maybe. Take the fucking molly, Papyrus.”  
  
And...okay, maybe it's because it's their graduation night. Maybe it's because there's this strange thick palpable nostalgia just sitting in the back of the throat Papyrus doesn't even have, cloying and far too sweet. Maybe it's the fact that they've been passing a bottle back and forth for the better part of an hour while Papyrus worked, matching each other shot for steadily-warming shot.   
  
Maybe it's the fact that the wicked smile Undyne flashes at him is this hungry, feral thing he's never seen on her before. Maybe it's because that sets something sharp and distinctly uncomfortable aching in the pit of his stomach.   
  
Maybe it's because there's a very real possibility that six months from now, Undyne and her scars and her conspiratorial grins will be off to the Academy while Papyrus remains behind, lives out his whole wretched life in the shadow of a glorified lab rat while she...well, while she takes top command in the Guard, probably. Surrounds herself with the kind of people worthy of that station.   
  
Forgets about him entirely.  
  
He doesn't know why he does it, is the point, but none of it actually matters for very long.  
  
Papyrus takes the fucking molly.  
  
  
  
  
  
*  
  
  
  
  
  
  
  
  



	2. Chapter 2

**Summary for the Chapter:**

> the basement
> 
> im sorry
> 
> i'm gross
> 
> come yell at morelikeskelesinstwopointoh.tumblr.com or vstheworld.tumblr.com
> 
> edit: and yes, it's been brought to my attention that I've somehow forgotten my own headcanon and contracted a previous fic. edits will be made....eventually.
> 
> sorry for being an awful stoner lol

[before]  
  
  
That Time in the Basement—and he always thinks of it like that after, capitals and all—isn't even close to the first time he's caught them.  
  
It's the first either of them knows about, probably, because Papyrus is small and limber and very good at hiding in small spaces, and also at being quiet when he really has to, if only then.  
  
He can't hear anything if he isn't, after all.  
  
The _actual_ first time he thinks he was maybe seven or eight, way too young for him to really have anything more than a vague concept of what two monsters might do in a bedroom alone together.  
  
He was certainly old enough to be curious where sans disappeared to every night after he thought Papyrus was asleep, though, because sans rarely left his side during his waking hours. His caretaker was a constant, near-silent shadow always lagging a respectful, irritating few paces behind, no matter how shrilly Papyrus demanded to be left alone. Even at home, he trailed vaguely after Papyrus unless directly ordered to do otherwise, which made Papyrus wonder—  
  
—what could _possibly_ be so much more important than him, anyways?  
  
So he followed his brother once, waited a full, squirming fifteen seconds before he padded down the hall carpet in the same direction, towards the only other room on the floor.  
  
Dad's room. Of course.  
  
That's clearly where he'd gone, too, because a warm glow still seeped under the door, the familiar yellow of Dad's favorite reading lamp. And it wasn't—look, Papyrus wasn't _scared_ of his father, per se, he wasn't a babybones anymore, but.  
  
He'd just never heard sans make that sound before.  
  
“Hush,” he heard his father rumble, barely audible through the heavy wood of his bedroom door, but it did nothing to stifle the low, wrecked kind of whine, repeated again and again and _again_ in a rhythm he won't really understand until he is much, much older.  
  
This first time though, it made something hot and slick squirm in the very pit of his soul, this distinctly uncomfortable twisting that had his meager dinner threatening an abrupt reappearance in the back of his throat. This first time, it sent him scrambling frantic back to his own bedroom, heedless of the way his bare-boned feet pounded on the hall carpet. This first time he hid under his dingy comforter and stared into the black expanse of nothing before him and just _shook_ until the door creaked open again, until his brother's slumped, familiar form slunk back into the room to curl up on the floor next to Papyrus's bed.  
  
If it was at all unusual for Papyrus to scoot himself closer to the edge of the mattress so he can lay one hand on sans's damp, flushed skull, neither of them chose to address it aloud. If sans was surprised that Papyrus's small, bruised fingers began to hesitantly stroke the cracked expanse of his brother's parietal bone, all the way down to the sharp slope of the occipital, he didn't comment.  
  
“thanks,” he husked after a few long, dragging minutes.  
  
Papyrus didn't say anything, but he also didn't stop petting him until sans's breath evened out into its usual faint, nasal rattling interspersed by the occasional awful snore.  
  
  
  
*  
  
  
[later]  
  
The weird thing is, sans doesn't fight it until he actually sees Papyrus coming down the stairs.  
  
He doesn't do anything at all in those long, muffled minutes Papyrus hovers at the landing, crouched to peek around the corner of the railing. He's hidden mostly from view in the relative dim outside of the brilliant white nucleus of the surgical lamps, so long as he doesn't let his eyelights flicker to life.  
  
sans doesn't say a word, doesn't resist when a pair of Dad's ancillary hands reach for his femurs and nudge them none-too-gently apart. Doesn't so much as whimper when a third sinks two fingers deep into the ruddy crimson-black glow of the magic, coalescing between his legs, though his hips jerk a little, startled.  
  
Papyrus breathes a sigh of relief between teeth he hadn't actually realized he'd been gritting. With his eye sockets blank and hollow like that, the rest of his body held stock-still under the absentminded assault of his creator, sans looks very nearly dead. Looks pathetic, anyways, all tiny and limp on the massive steel table. As much as the wet, slick sounds emanating from the bottom of the staircase might turn Papyrus's stomach, the minute flinch sans gives at each cruel thrust is at least a reminder that he's still breathing, kind of.  
  
This meshes, at least, with what little porn he'd been able to work his way through during his handful of furtive, blushing searches on the undernet—he usually had to turn it off out of sheer embarrassment not a full minute in, so he'd really only made it past the preparation stages twice that he recalls.  
  
So this...makes sense, kind of, preparing a partner for the second act, and it's not like he didn't _know_ his father had been taking his creation to bed. He'd heard them, hadn't he, all those months and months ago, but...that had always been through closed doors. That had been the same kind of noise, even—slick, kind of like spaghetti being stirred, he thinks absently, absurdly. His empty stomach is far easier to think about than the yawning pit that opens in the center of him when he finally realizes that sans is strapped down to the table, pinned like a bug to cardboard. It's the same urgent groan, anyways, the same kind of hitching, ragged breath from his pseudo-brother.  
  
It's not anything like the sounds the monsters from the porn made though, those weirdly rhythmic squeals that didn't sound quite right even to his untrained ear. It's low, wrecked noises under his breath, nearly animal in register, never once approaching actual words.  
  
sans is practically panting by the time Dad slips a third finger in, and his head slams back onto the table, neck snapped tight in a painful-looking arc. His teeth are parted just enough for Papyrus to see the faint glimmer of his rust-colored magic on the silver bar Papyrus had given him for Gryftmas last year.  
  
He recognizes this now. He knows, intimate, the exact pitch of that frantic breath through a twice-broken nasal cavity. He's been listening to it for _years_ , after all, hasn't he?  
  
He wishes he'd never known that his brother— who'd once grabbed the edge of a hot baking sheet bare-clawed, and not even registered the pain until his fingerbones began to burn, until Papyrus snatched the thing away with gloved hands and snapped _the fuck is wrong with you, get that under some water you_ freak— screws his eye sockets closed, wincing while it happens. Wishes he'd never seen his brother sink his mismatched teeth into the cracked line of his own ulna and bite down _hard,_ choking down something unnervingly like a sob as the wide, bony thumb shoves itself up against what has to be his clit, judging by the frantic whine it wrenches out of him.  
  
He'd always liked that sound, too.  
  
Now, Papyrus stuffs two knuckles into his own mouth and bites 'til his mouth floods with the coppery taste of his own blood. It's clear conscious echo of the way his brother seems determined to bite straight through half his arm, partially to muffle the horrified wail threatening in his throat, partially because _he had liked that sound_. And that sound was sans hurting, so. What better way to train his own brain to avoid the topic entirely, than to associate pain with the noise?  
  
It's only rational. Logical. Basic behavioral science, really, a simple enough concept that even a monster dull as Papyrus can easily grasp it.  
  
Dad isn't even looking at sans, which is the weirdest part. He seems to be logging something on a nearby display with the hands that are still attached, clipboard clenched tightly in his claws and eyelights fixed to the screen. He's got two more hands adjusting the temperature on some sort of liquid sitting over an open burner, and the remaining three, well.  
  
Papyrus isn't really sure what he expected here, but it certainly isn't _this_. His class had been careful to cover the many dangers of reproduction—brainwashing, Dad always called it, a laughable attempt at population control—but his teacher hadn't really touched on anything applicable here. He's not even sure if she could have, honestly, since she had twenty-five students, all of different species, with, Papyrus assumes, a much different approach to the topic than his own kind.  
  
It's a little odd that sans has a cunt to begin with. He's always used masculine pronouns, as far as Papyrus knows. When Dad doesn't forgo gender entirely, anyways, and stick with the cold, clipped “it” he'd used when he had first brought sans home.  
  
Regardless, he'd always seemed...well, like a _he_. So, from Papyrus's limited understanding, his magic should have naturally formed male organs, should have defaulted to a cock, even if his partner was working with the same kind of equipment, right? Maybe an entrance, to accommodate said partner, but--  
  
Maybe sans just has a lot of experience. Maybe his magic is so attuned to this that he can change it at will. Maybe in the years before sans had a name and a place to sleep and real clothing all his own, he'd been subjected to the same thing.  
  
Maybe back in the lab--  
  
Dad neatly derails that particular train of thought, though, when he calls over one shoulder, “Come here, Papyrus. There's no point to hiding if you're going to do it that poorly.”  
  
“I...don't understand,” Papyrus says softly, but he approaches as ordered. Almost without meaning to entirely, really, his body gravitating towards the sterile gleam of surgical lamps and the familiar droning voice of the only real family he's ever had.  
  
Dad barely glances up at him, eyelights just briefly meeting his over the top of the clipboard. Slowly, he arches one brow. “What don't you understand, Papyrus,” he says, every word even and measured and as bland as if he'd been addressing a particularly slow lab tech. It is very patently not a question.  
  
Papyrus looks over at the table, the words catching sharp in his throat like he had swallowed something wrong. sans's face is twisted away from him now, buried in the meager shelter of his own shoulder, but he's also flushed and sweating halfway down his sternum so it doesn't hide as much as he'd probably hoped. Doesn't do a thing for the way his legs are still pinned neatly apart, one hand on each scuffed kneecap, though Papyrus is careful to keep his eyelights firmly away from the dark pulsing of magic between those greyed femurs.  
  
“please stop,” sans is murmuring to himself, low, this constant, rhythmic loop like a mantra, but he doesn't seem terribly intent on Gaster hearing. “please stop, please stop, please _stop_ — “ and then he twists, abrupt, actually thrashing in his bonds frantically. His untethered tail snaps hard against the steel table with a resounding _clang_ that echoes in the dim basement chill. Papyrus jumps.  
  
“you complete _bastard_ ,” sans snarls with a vitriol Papyrus has never heard from him before, whipping his head around to fix furious eyelights on Dad. He slams his own skull into the metal, possibly to emphasize his point, and bares his teeth, jagged edges illuminated by a mouthful of crackling pink magic. “you promised me, you said if i behaved, you _said— “_  
  
What, exactly, Dad had said to him on this particular topic, Papyrus never finds out. A new hand pops into existence maybe six inches from sans's head in an apathetic little crackle of purple magic, and proceeds to shove four bony fingers lengthwise between parted fangs without seeming too terribly bothered about the whole thing, not even when he snaps down on them _hard_.  
  
Papyrus winces at the ceramic grate of canine meeting metacarpal but Dad doesn't actually seem to feel it at all. And maybe it's because he can't feel it that he presses them in just a _little_ bit too hard, just enough to make sans's face flush even redder as he chokes on them.  
  
Maybe.  
  
“You were saying,” Dad prompts, turning back to his screen as the hold loosens enough for sans to pull shallow, shuddering air into whatever passes for his lungs. The fingers stay where they are though, prying that stubborn jaw open and Papyrus just kind of stares, unblinking, as a thick strand of pinkish saliva slides down the palm to drip off the neat, abrupt termination of the wrist.  
  
His mouth is suddenly dry as sandpaper, though he can't remember really noticing what it felt like very much before this immediate second. “What are you doing to him?”  
  
And Dad, despite the fact that he now has four fingers shoved up into the flushed, flickering magic of the closest thing Papyrus has to a sibling, despite the way two more of his conjured hands pin sans's legs to the table at an angle that would probably rip tendons, if he had any—  
  
Dad only tips his head half a degree to one side and says, “Routine maintenance,” like it bores him.  
  
sans whines as the fingers begin, slowly, to push into him at a kind of lazy, cruel pace—they pull out nearly entirely with this kind of gentle squelching sound that should, by all rights, be ridiculous. It's too loud and it's _awful_ , thick and sticky-wet and absolutely impossible to ignore in the empty bite of the basement's relative quiet. It's got to be the least arousing thing he could _possibly_ be focusing on here, and it should, by all rights, make him wrinkle his nasal cavity in disgust at the absurdity  
of it alone but instead— the sound hits Papyrus oddly low in the base of his spine with this creeping, uncomfortable heat.  
  
The fingers slip easily back inside sans despite the way he's still kind of mechanically shaking his head. They don't really hesitate, don't pause at all when he sucks in a sharp breath at the intrusion, just shove themselves deeper, 'til he actually keens in protest, 'til they're buried inside him nearly to the knuckle. The thumb's at a good angle to rub little circles into his clit from there and it _does_ with a kind of brutal efficiency, which at least cuts off his terrible, reedy wailing. Weirdly, the flush of sans's magic seems to pulse brighter at the touch, only for a moment, his pelvis hitching minutely up into the pressure.  
  
The sound he makes when the fingers begin to shallowly fuck into him, though, each one braced _just_ far enough from its neighbors that the intrusion looks distinctly uncomfortable even to the untrained eye, his garbled attempt at managing something like speech through the choking bracket of Dad's conjured fingers...  
  
It sounds an awful lot like the word _no_.  
  
Papyrus shivers.  
  
“He— _why_ , though?” he presses, for no actual good reason he can think of. Dad has made a very clear delineation of where Papyrus's opinions are welcomed, and the lab is not one of them. That had been determined the very first time Papyrus, seven years old and shaking with nerves at his father's eyelights tracking him for the longest stretch of time his young mind could recall, had knocked a very delicate experiment into its own burner with an errant elbow, nearly setting half the lab on fire as an added bonus. “What did he _do_?”  
  
Because sometimes—and not _always_ , he's not entirely stupid, he sort of learned to pick up context from watching other kids and their respective guardians, since Dad seems to nearly reign his treatment of Papyrus into some parameters of acceptable parental discipline—sometimes Papyrus makes the very same mistakes as sans.  
  
Sometimes he fucks up just as badly as his not-brother. Sometimes he's the one that trips and he's got the crack across the bridge of his nasal cavity to prove it, the ring of deep bruising around his right humerus where Dad's fingers had snagged him in a vise grip and held, for some minor crime he's already forgotten about. He's dimly aware that this is _probably_ one of those things he should absolutely know his father would never do to him, but.  
  
Still never hurts to play it safe these days.  
  
“Dad,” he says, snaps it maybe a little too sharply at his father when he receives nothing at all in response to his question.  
  
“Hmm?” Dad blinks, almost like he'd forgotten Papyrus was there, which isn't entirely out of the realm of possibility. He'd been staring at the screen again, distracted by nothing that makes any sense to Papyrus, this baffling readout of pulsing, spiky lines.  
  
“What did sans do?” Papyrus repeat.  
  
This time, his thinks there might be an edge to his voice, some hint of the irritation that thrums in his not-eardrums at being ignored, because his father's eye sockets narrow behind the half-moons of his glasses. Dad draws himself up to his full height, peering down at Papyrus as though he's a particularly interesting insect the scientist had happened across on the sidewalk. “I answered your question,” is all he says though, his tone bored and flat as if they were discussing this week's shopping list. “Sterilization on this particular species can be...complicated. Simpler to manually relieve its tension whenever the need arises.”  
  
And then.  
  
And _then_.  
  
“You know,” Dad says, and there's this horrible new spark of interest in it, this note of heated curiosity Papyrus doesn't think he's heard directed at himself since he was a child, “I...suppose it's about time you get more hands-on experience with it.”  
  
_And then._  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  
  


**Notes for the Chapter:**

> noncon all over the place, bondage, choking, vaginal fingering, Gaster is the worst and Papyrus isn't a lot better, someone save Red

**Author's Note:**

> not a lot here, but we're leading up to some real gross stuff.


End file.
